Seasonal differences of the atmospheric particle size distribution in a metropolitan area in Japan

► We measured the particle number concentrations as a function of distance from road. ► The particle number concentrations were observed to be decaying with distance. ► The decay rate depended on season and particle diameter. ► The spatial distribution of < 30 nm particles strongly depend on seasonal temperature. ► Mass-transfer theory suggests that it is due to evaporation of semivolatile materials.